Means for stabilizing film in a sound translating apparatus



Oct. 25, 1955 E. P. KENNEDY 2,721,738

MEANS FOR STABILIZING FILM IN A SOUND TRANSLATING APPARATUS OriginalFiled Oct. 28, 1947 IN V ENTOR.

$5 Adar/ 0.

United States Patent IVIEANS FOR STABILIZING FILM IN A SOUND TRANSLATING APPARATUS Edward P. Kennedy, West End, N. 1., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Army Continuation of abandoned application Serial No.782,665, October 28, 1947. This application July 6, 1950, Serial No.172,377

2 Claims. (Cl. 271-23) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental purposes, without the payment of anyroyalty thereon.

This application is a continuation of abandoned application SerialNumber 782,665, filed October 28, 1947.

This invention relates to a new and useful means for stabilizing film ina sound translating apparatus, particularly of the sound reproducingmotion picture film type and has for its principal object the provisionof a stabilizer which is positive in its operation of stabilizing themoving film, thereby to reduce to a minimum film disturbances whichotherwise occur through ineffective stabilization of the film.

Another object of the invention is to provide an arrangement of theclass hereinafter described which is relatively light in weight and onewhich dispenses with the employment of a heavy inertia fly wheel. Thearrangement for elfectively and positively, with the maximumsensitivity, stabilizing the moving film as it is passed onto and shedfrom the sound drum, may be said to be composed of three distinctcomponent parts which function at times as indiivdual units, and inpairs, and all together, to bring about stability and uniform filmvelocity past the sound drum.

A further object of the invention is the provision of this method andmeans for dissipating and/ or reducing to a minimum many of the commondisturbances which are present in motion picture projecting and soundreproducing apparatuses, some of the common disturbances beinggear-train teeth impulses, sprocket teeth impulses, film slippage aboutthe sprocket teeth, sprocket cam action due to eccentricity, artificialrun-outs caused by lumps of foreign matter collected on film surfaces,film splices, take-up reel disturbances, or any combination oraccumulation of all these disturbances.

Yet a further and equally important object of this invention is theprovision of an arrangement of parts hereinafter described which ishighly sensitive in its function of stabilizing the film upon thepresence of any irregularity in the action or movement of the film whichwould otherwise function to bring about instability of the film.

A further object of the invention is to reduce to a minimum the numberof precision parts, and at the same time to improve the output over muchmore costly arrangements.

Other objects will appear more fully hereinafter.

The invention consists in the novel combination and arrangement of partsto be hereinafter described and claimed.

The invention will be best understood by reference to the accompanyingdrawings showing the application of my invention, and in which:

Fig. 1 is a fragmentary sectional detail view of a motion pictureprojecting and sound reproducing apparatus showing my inventionincorporated therein; and

Fig. 2 is a fragmentary detail view of the reverse side of that shown inFig. 1.

2,721,738 Patented Oct. 25, 1955 Referring now more particularly to thedrawings, 10 indicates a body plate of a motion picture projecting andsound reproducing apparatus of a standard and conventional constructionwhich includes the exciter lamp 11, a scanning lens 12, and a sound drum13, all of which parts are related one to another in a manner well knownin the art. Together with a photocell this constitutes a soundtranslating device responsive to the sound track. The drum 13 is adaptedto carry the film 14 on which is present the usual sound track. Thisfilm, as shown in the drawings, passes around an idle roller 15 arrangedadjacent a feed sprocket 16 having the usual sprocket teeth 17 whichengage the perforations of the film and having associated therewith theusual and conventional pad roller 18.

From the feed sprocket 16 the film passes around the sound drum 13 andis rolled into close facial contact therewith by impedance roller 19pivotally supported as at 20 to the body plate 10 of the apparatus. Fromthis sound drum 13 the film is fed over a take-off sprocket 21 similarto the sprocket 16 and likewise provided with sprocket teeth 22, adaptedfor engagement with the film perforations. From sprocket 21 the filmpasses over and around idle rollers 23 and thence to the film take-upreel (not shown).

Associated with the shaft 24 carrying the sound drum 13 is an inertiawheel 25 which by reason of the employment of my improved method andmeans of stabilizing the film in its passage around the sound drum, maybe constructed relatively-light in weight.

The shafts 26 and 27 carrying the sprockets 16 and 21, respectively, areconnected together by intermeshing gears 28 and 29. On the shaft 26 is adrive pulley 30 driven by means of a suitable belt 31 in a manner wellknown in the art. In lieu of this belt 31 there may be employed a trainof gears for the purpose stated.

The body plate 10 has connected thereto in any suitable manner pintleshafts 32 and 33 in parallel spaced relation with respect to each otherand other axes of the film carrying elements. Pivotally carried by eachof these shafts 32 and 33 are arms 34 and 35 which are shown of the sameform, and may be of approximately the same weight. The outer extremitiesof these arms 34 and 35 rotatably support rollers 36 and 37, which,under conditions to be hereinafter explained, will effect stabilizationof the film upon the presence of one or more of the common disturbanceshereinbefore set forth. The arms 34 and 35 extend generally along thepath of those portions of the film against which the rollers 36 and 37will rest in operation, so that the rollers will move approximately atright angles to the film path as the film tension varies due to anycause.

It will be noted that the feed sprocket 16 is arranged with respect tothe film 14 and the sprocket 21 so that with the film on the teeth ofone sprocket and stretched taut around the sound drum 13 to the othersprocket it will not register with the teeth but must be loosenedapproximately one-half frame. This arrangement assists in properthreading and, of itself, governs the minimum length of the film pathfrom the sprockets to and around the sound drum, whereby if the film ispulled tight at either sprocket position, the sprocket teeth will notengage the film perforations until the film is slacked off one-halfframe or approximately .150 inch. This slack is desirable and necessaryfor the reason that it provides a sufiicient length of slack film whichwill form into the natural film loops or bowed bights a, b, c, d, e, f,g, and h, when the film is partially tightened by the weight of therollers 36, 37, all of which bights are necessary to the systems properfunctioning. This slack is also desirable for the reason that itprovides sufficient latitude in the interposed film length to allow forall usual degrees of film shrinkage, a factor that has to beaccommodated for by film propelling systems. The natural position ofthese film loops is such that the force of each roller is balanced bythe pull of its portion of the film and the pull of each portion is alsobalanced around the sound drum. If the film elasticity is ignored, thesituation is analogous to a loaded clothesline with a pole at thecenter, except that the sound drum has substantial inertia; each portionof line or film will have sufficient sag to support its load at the pullrequired for the combination.

The film material has certain properties very significant to theoperation, particularly the combination of properties known asviscoelasticity which tends to make the film substantially straight, andyet return slowly toward such a straight form when bent, as discussed inFundamentals of Plastics by Richardson and Wilson, McGraw Hill 1946, p.408. The latter or viscous aspect is utilized for damping outoscillations which might otherwise occur from the weights and the actualelasticity of the film bowed bights, used to absorb high-frequencydisturbances, or the somewhat elastic property of changes in forcevectors as the film path changes, used to absorb low-frequencydisturbances in starting or running. When the viscosity is opposed tothe elasticity the effect known as elastic memory can be observed in theslow creep of the material back to its stable form. The viscosity may bemodified by temperature and under certain extreme conditions even theelasticity may be altered to provide a new stable form.

When the apparatus starts in motion the lower web 39 of the film isdrawn relatively tight by the rotation of the sprocket 21 while thesprocket 16 is feeding out the film at the same rate as the sprocket 21is taking up the film. The sound drum is therefore energized by the pullthus created because the impedance roller 19 is enforcing compliancebetween the film and the drum, and in time this will bring the drum andinertia wheel up to the film velocity being imposed upon it. During thisoperation the roller 37 has been forced to assume a maximum upperposition against the downward pull due to gravity. Meanwhile slack hasaccumulated in the upper web 38 of the film, which allows the roller 36to be pulled by gravity into its maximum lower position. During theperiod that the inertia wheel 25 approaches a velocity which correspondsto that of the film, the film supplies constantly decreasing amounts ofenergy to it, until there arrives a time when it is called upon to supply only the minute supply of energy necessary to overcome the overallfriction. During this period, the rollers 36 and 37 are constantlyassuming new positions interposed by the constant downward pull ofgravity on them accompanied by corresponding changes of forcedistribution in the loops 38 and 39. As the roller 37 takes a lowerposition, the roller 36 is constrained to take a directly opposite,higher position, and so on, both moving simultaneously in oppositedirections until a condition has been arrived at when the resultant ofall opposing forces on either side are reduced to equality. When thiscondition is satisfied, teetering ceases and the film travels in astable condition unless and until disturbances upset the establishedbalance in either or both of the webs 38 and 3?. Such disturbances causethe film Webs 38 and 39 and the rollers 36 and 37 to transfer theirenergy through the gravity-coupled rollers from one side to the otherand vice versa, via the inertia wheel if the disturbance is ofsufiicient magnitude.

After the dissipation of such disturbance, the bights a to 11 inclusiveautomatically tend to assume their normal shape, and stability is againrestored when a condition is reached where each repeated energy transferfrom one side to the other has been reduced to the point of absorptionand dissipation through the presence of the combined viscosity of thefilm loops 38 and 39 working together with the combined friction of theentire operative portion of the apparatus. Also inherent in the film isa certain amount of elasticity. The various forces due to elasticity andgravity, the masses of the elements, losses due to friction andviscosity, and vibrations due to sprocket teeth and their driving gears,could involve a very complex mathematical analysis; such analysis isunnecessary in view of the substantial value of the viscosity whichdissipates the vibrational effects. Similarly the proper positions foraxes 32 and 33 may be calculated but an empirical determination of theconditions giving best results and suited to the arrangement of theother parts is the most practical solution of the problem. In thismanner it will be seen that most minor disturbances are absorbed by therollers 36 and 37, or either of them, and the film webs, before suchdisturbances reach the sound drum. Stated another way, the balancedgravitational arrangement of the rollers which utilizes the mechanicalfriction and the viscosity characteristic of the film bights, issomewhat independent of the inertia wheel itself in dealing with all butmajor disturbances, such as film splices, dirt, lumps and the like uponthe film.

It will be apparent that the physical characteristic behavior of thefilm, in either the upper or the lower web, is identical and thereforeintroduces no unlike components of its own.

As indicated before, the gravity-urged rollers 36 and 37 are of selectedsize, weight and position and travel through selected radii. Thesecommon system members are chosen with respect to the vectorial forceresolution patterns which they will produce when they combine to joinforces with the viscosity and compliance characteristics of the filmloop bights a to h inclusive. These bights occur in the semi-slack filmloops interposed between the rollers and their provincially associatedsprockets. The bights in the upper and lower film loops interposedtoward the sound drum, serve to semi-isolate the sound drum duringperiods of minor film disturbances occurring between the rollers andtheir associated sprockets.

One of the advantages of my method and means of stabilizing results inpermitting employment of an inertia Wheel of relatively light weight, inaddition to the many advantages hereinbefore set forth.

While I have illustrated and described the preferred form ofconstruction for carrying my invention into effect, this is capable ofvariation and modification without departing from the spirit of theinvention. I, therefore, do not wish to be limited to the precisedetails of construction set forth, but desire to avail myself of suchvariation and modifications as come within the scope of the appendedclaims.

Having thus described my invention, what I claim as new and desire toprotect by Letters Patent is:

l. A sound film translating system comprising a rotatable sound drum ofsubstantial inertia on which a perforated film, of substantial bendingelasticity and viscosity and carrying a sound track, may be moved withthe track in operating relation to a sound translating device,synchronized sprocket means for feeding film to and taking film fromsaid drum at substantially identical rates, the minimum distance alongthe path of a film around said sound drum to the teeth of said sprocketmeans at each side of said sound drum being intermediate to the distancebetween an integral number of perforations of said film, to require thatsaid film be slacked off to register with said teeth, roller means ofsubstantial translational inertia resting resiliently, with only theforce due to its weight on said film between said drum and said sprocketmeans on each side of said drum, said force serving only to partiallytighten said film and to produce substantial bowed bights from theremaining slack on each side of said sound drum, an impedance roller toforce said film into contact with said drum, whereby under steadyrunning conditions vibrations transmitted to said film by said sprocketmeans are dissipated in the viscosity of said film at said bights, andsubstantially equal loops are maintained by said roller means in saidfeed and take-off portions of said film, and under starting conditionsoscillations due to inertia and elasticity are also dissipated in saidviscosity.

2. A sound film translating system comprising a rotatable sound drum ofsubstantial inertia on which a perforated film, of substantial bendingelasticity and viscosity and carrying a sound track, may be moved withthe track in operating relation to a sound translating device,synchronized sprocket means for feeding film to and taking film fromsaid drum at substantially identical rates, the minimum distance alongthe path of a film around said sound drum to the teeth of said sprocketmeans at each side of said sound drum being intermediate to the distancebetween an integral number of perforations of said film, to require thatsaid film be slacked ofi to register with said teeth, roller means ofsubstantial translational inertia resulting resiliently, with a force ofthe order of its weight, on said film between said drum and saidsprocket means on each side of said drum, said force serving only topartially tighten said film to produce substantial bowed bights from theremaining slack on each side of said sound drum, an impedance roller toforce said film into contact with said drum, whereby 25 under steadyrunning conditions vibrations transmitted to said film by said sprocketmeans are dissipated in the viscosity of said film at said bights, andsubstantially equal loops are maintained by said roller means in saidfeed and take-0E portions of said film, and under starting conditionsoscillations due to inertia and elasticity are also dissipated in saidviscosity.

References Cited in the file of this patent UNITED STATES PATENTS Re.19,270 Kellogg Aug. 14, 1934 1,831,562 Heisler Nov. 10, 1931 2,013,109Reynolds Sept. 3, 1935 2,108,337 Hoifman Feb. 15, 1938 2,251,322Buhrendorf AuguS, 1941 2,416,606 Zimmerman Feb. 25, 1947 2,442,400Collins June 1, 1948 2,499,210 Bartelson Feb. 28, 1950 FOREIGN PATENTS370,001 Great Britain Mar. 24, 1932 477,943 Great Britain Jan. 10, 1938582,180 Germany Aug. 10, 1933 753,206 France Aug. 7, 1933

